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arXiv 1306.2490cond-mat.mes-hallcond-mat.str-el
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$Fe_{3}O_{4}$（111）/ $Alq_{3}$ /Co自旋阀器件中注入到隧穿导电模式的交叉及相关磁阻

Crossover from injection to tunneling conduction mode and associated magneto-resistance in a single $Fe_{3}O_{4}$(111)/$Alq_{3}$/Co spin-valve device

P. Dey, R. Rawat, S. R. Potdar, R. J. Choudhary, A. Banerjee

备注：
GMR to TMR changeover across Verwey transition of the electrode in a single spin-valve device
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摘要：

在$Fe_{3}O_{4}$（111）/ $Alq_{3}$ /Co垂直自旋阀（SV）器件中，利用$Fe_{3}O_{4}$电极Verwey相变对能带结构的改变，实现了界面能级工程.器件特性（I-V）研究的实验结果表明，在$Fe_{3}O_{4}$电极的Verwey转变温度（$T_{V}$）范围内，导电模式从载流子注入转变为隧穿。在单个SV器件中，分别在低于和高于$T_{V}$的温度下观察到巨磁电阻（GMR）和隧穿MR（TMR）随温度的变化。巨磁电阻的出现，以及注入受限的自然Schottky型I-V特性，为该SV器件中电极/ $Alq_{3}$界面的自旋注入和分子轨道输运提供了证据。TMR的特征与GMR的特征有很大的不同。这是由于在多步隧穿机制中占主导地位的超精细场相互作用。我们已经实现了室温SV操作在我们的设备。已经提出了一种用于器件操作的唯象模型来解释跨$T_{V}$的传导模式和相关MR特征的转变。我们提出，在费米能级上的电荷间隙的调整跨Verwey转变由于电荷在$Fe_{3}O_{4}$的八面体铁网站上的结果在相应的导电模式的调整，导致这种独特的交叉从GMR到TMR在这种铁氧体基的有机SV。

英文摘要：

We demonstrate interface energy level engineering, exploiting the modification in energy band structure across Verwey phase transition of $Fe_{3}O_{4}$ electrode, in a $Fe_{3}O_{4}$(111)/$Alq_{3}$/Co vertical spin-valve (SV) device. Experimental results on device characteristics I-V) study exhibit a transition in conduction mode from carrier injection to tunneling across Verwey transition temperature ($T_{V}$) of $Fe_{3}O_{4}$ electrode. Both giant magneto-resistance (GMR) and tunneling MR (TMR) have been observed in a single SV device as a function of temperature, below and above $T_{V}$, respectively. Appearance of GMR, accompanied by injection limited natural Schottky-like I-V characteristics, provide evidences of spin injection at electrode/$Alq_{3}$ interface and transport through molecular orbitals in this SV device. Features of TMR exhibit significant differences from that of GMR. This is due to the dominant hyperfine-field interaction in the multi-step tunneling regime. We have achieved room-temperature SV operation in our device. A phenomenological model for device operation has been proposed to explain the transition in the conduction mode and associated MR features across $T_{V}$. We propose that the tuning of charge gap at Fermi level across Verwey transition due to charge ordering on the octahedral iron sites of $Fe_{3}O_{4}$ results in a corresponding tuning of conduction mode causing this unique cross over from GMR to TMR in this ferrite-based organic SV.

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